text:
How do stealth aircraft operate from rough or contaminated fields without ruining their paint jobs?
While thinking about the MiG-29’s dedicated rough-field intakes, I started wondering about rough-field operations for other types of combat aircraft, and, naturally, since most new combat aircraft designs are stealth aircraft...
...how do stealth aircraft, with their fragile radar-absorbent coatings, operate from rough or contaminated fields (such as basically any frontline bases, which they would have to operate from in a war of equals,1 given that launching from rear-echelon airbases and then refuelling over the combat zone isn’t possible in such a situation, seeing how flying a tanker somewhere you don’t have air supremacy is merely a rather expensive method of suicide) without the attendant sand and grime and rain and hail and discarded shrapnel and whatnot quickly rendering them non-stealth?

1: A full-scale war between the United States and China, for example.

I'm not an expert by any means but as far as I know the stealth characteristics are not only achieved by the surface coating, I think a major factor is the geometry of these aircraft. A lot of the surfaces are at an angle to avoid reflecting the radar waves back to the direction they came from. And a bit of dirt is probably not going to change that geometric shape... but that's just my idea here.

Most of your assumptions are incorrect. I would recommend doing your homework about this first and then coming back to rephrase the question. For one thing, air refuelling for aircraft operating in the front lines of a conflict is a commonplace occurrence. Also, the coatings on "stealth aircraft" are not something I would describe as "fragile."

@JuanJimenez: 1) Frontline aerial refuelling is indeed a commonplace occurrence... when fighting opponents with no air force or air defences to speak of.  2) Given that said coatings can be damaged by flying through rain...

https://www.amc.af.mil/News/Article-Display/Article/147242/vietnam-the-first-tanker-war/ 2) You forgot to mention that the Air Force has denied that.

@JuanJimenez: 1) Were those tankers actually routinely flying over North Vietnam, though, or were they loitering over the South China Sea?  2) Air Force denies something embarrassing to them, so, of course, it never happened.  Riiiiight...

Both. 2) Media reports something on the Internet, so of course, it must be true. Riiiight. Reminds of a certain company's advertisement featuring French models. :)

I don't understand. You're proposing to have an air field with a dodgy runway that's close enough to the action that your stealth aircraft can perform their mission from there without refuelling. If that place is safe enough to put planes on the ground, isn't it also safe enough that you can refuel in the air immediately above it?

Seeing as the B-2 can't even operate in rainy weather without its billion dollar paint job getting ruined (maybe they've solved that problem by now, but it was a real concern) I seriously doubt any thought was given to operating them from unprepared strips in combat zones. F-117 ditto, special tents had to be constructed in Saudi during Desert Shield to house those.

Yeah @JuanJimenez is right. For example, the F-35, there are special mats of material that provide stealth, fighters like the F-22 use a combination, but most future stealth aircraft are being designed with mats mainly. This would be much more resistant to debris.

@DavidRicherby: Safe enough for the fighters?  Yes.  Safe enough for the tankers?  Not necessarily.

@Sean If it's safe enough for an air base, isn't it safe enough to fly tankers over it?

@Sean You seriously are not aware that tankers do not operate solo at any location?

I think you're working off some incorrect assumptions.
Firstly the "fragile radar-absorbent coatings" you refer to aren't quite the issue you think they are - yes the B-2 is famously something of a garage queen (famously requiring climate controlled hangars and suffering a degradation in the stealth performance with each flight) and essentially cannot be deployed to a "rough field" base such as you describe. The thing with something like the B-2 though is that it doesn't need to be - its range (6,000 NMi, or 10,000 with one refueling) means it just flies from Andersen or from Whiteman etc.
Even the B-2 however is not solely reliant upon the Radar Absorbant Material (RAM) coating for stealth - a large portion of its reduced radar cross section (RCS) comes from its shape, and other stealth characteristics come from reduced heat, acoustic and visual signatures. "Stealth" is so much more than just slapping a coat of Dulux Radar Absorbent Paint[1] on any old jalopy you've got lying around.
More recent "stealth" designs (i.e. the "Fifth Generation" fighters) such as the F-22 have a further reduced reliance on RAM skins as the understanding of radar reflections and the technology to compute it have improved. The F-22 doesn't require the climate controlled hangars of the B-2 and can be operated and maintained out of "normal" bases and hangars. Could it operate out of a really rough field? Don't know - if the USAF has tried they haven't mentioned it that I know of. I believe it was deployed to bases in Malaysia for operations in Syria.
The F-35 takes this a step further - Lockheed say that some of the RAM is "baked in" to the skin of the aircraft, making it much more durable and slower to degrade and the coatings are supposed to cure much faster than those used in the F-22, reducing maintenance turnaround. The F-35 certainly seems fairly flexible in terms of the environments it can be deployed in - operating from carriers, the UK, Israel etc.
TL/DR: with the exception of the B-2 the RAM coatings on in-service stealth aircraft[2] aren't that fragile, aren't that hard to restore and aren't actually that important. And the B-2 would be extremely unlikely to ever need to operate out of the sort of base you describe in the first place.
[1] I don't think Dulux actually make RAM paint - but wouldn't that be a great talking point at dinner parties?
[2] I've not forgotten about the J-20, but the PLAAF hasn't exactly published much about it!


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Why/how is a downplane parachute configuration aerodynamically stable?
One of the most dangerous situations possible in skydiving is a so-called downplane, where both the main and reserve chutes deploy, and they shift outwards to the sides of the parachutist until essentially side-on, like so:

(Image by the United States Navy, via Wikimedia Commons; this is actually a simulation of a downplane, with two parachutists and only one parachute per parachutist, rather than the real deal, which would involve both parachutes deploying from a single parachutist, but it illustrates the configuration very nicely.)
This reduces the total cross-sectional area (as seen by the airflow) of the parachutist-parachutes assembly, causing said assembly to accelerate downwards to greater-than-optimal speeds, which is why a downplane situation is dangerous.
However, it is far from obvious how a downplane would be aerodynamically stable; even when virtually edge-on, each of the open parachutes still has a very high drag coefficient,1 a fairly low mass, and (as a result) a very low ballistic coefficient,2 while the skydiver attached to the parachutes has a fairly low drag coefficient, a much higher mass (relative to their parachutes), and, consequently, a very high ballistic coefficient.  As such, the parachutist should tend to trail ahead of the two parachutes, with the aerodynamic forces on the latter wrenching them up towards top dead3 center, unless the whole shebang is spinning rapidly enough about its vertical axis for the outwards centrifugal force on the parachute canopies to overcome the upwards drag force on said canopies, which would require a spin rate high enough to be lethal even without taking parachute malfunctions into account.
What is it that overcomes these aerodynamic forces on the parachutes and renders a downplane aerodynamically stable?

1: Albeit much lower than when face-on.
2: A measure of the relative unaffectedness by aerodynamic drag of an object moving through an atmosphere of given composition.
3: No pun intended.

The parachutes are both being pulled straight down from a single point.  That means the relative airflow, or angle of attack, is straight up.  Lift is perpendicular to the AOA.  Even if the parachutes are stalled at near 90 deg AOA at the beginning, there is still a bit of lift being produced, which acts at 90 degrees to the AOA, creating a net thrust component that causes the canopies to move away from each other, reducing AOA as they arc down, and as they become more unstalled by the reducing AOA, the lift force with net thrust component perpendicular to the AOA gets stronger, driving them away from each other harder and they arc down some more.
Eventually, as they move down to the sides, AOA continues decreasing and therefore the net thrust component of the lift force decreases, until it's small enough to be balanced by the drag of the canopies.
If the canopies move back up, AOA goes up, lift goes up, and the net thrust component goes up, driving them back down on their arc.  If they move farther down, the net thrust of the lift component declines enough that drag overcomes it and moves the canopies back up.  Somewhere in there, everything balances out.  You are in a stable equilibrium condition.

...So like how a kite can rise against the wind?

As long as the kite is at an angle less than vertical,  the wind striking it, at, say a 70 deg angle of attack will result in some lift being made even if it is fully stalled, just from the air striking the undersurface and being deflected.  The net lift force is aft and slightly up; the aft force component is applying tension to the string, and the up force component, while small, is enough to lift the kite vertically, and as it rises the AOA drops and it gets more lift until it reaches lift/drag equilibrium.

It appears that each parachute will tend to adopt a position where a line drawn from the skydiver through the center of pressure of the chute is aft of a line drawn through the skydiver perpendicular to the relative wind, by an angle equal to the L/D ratio of the parachute.  The higher the L/D ratio of the parachute, the closer to "straight overhead" the chute can be, in the reference frame of the falling skydiver with his body positioned horizontally as per the photo.  Much as the higher the L/D ratio of a kite on a string, the closer its steady-state position can approach a position straight "overhead" the kite flyer.  But a stable downplane should be possible even with chutes with a rather poor L/D ratio-- the chutes just wouldn't be positioned nearly opposite each other as is the case in the photo.  This would be analogous to a kite with a poor L/D ratio flying in a position that is far from "overhead" the kite flyer.  The speed of such a downplane would tend to be lower than the downplane illustrated in the photo.

(A diagram would help.  PS this answer was apparently being typed and posted simultaneous w/ the other recent answer-- )

The parachutes are in a high lift position, pulling opposite each other and so holding the parachutist up. If the parachutist drops lower, he pulls the parachutes into a higher AOA, which gives more lift, and it pulls the parachutist back up. Thus, it is stable.

If the parachutes are pulled to a higher, liftier angle of attack, shouldn't that result in them (the parachutes) being pulled even more strongly towards top dead center, and moving even further above the parachutist?

@Sean For an aircraft (such as a skydiver) which is moving straight down through the air, lift is the horizontal aerodynamic force and drag is the vertical aerodynamic force. (This is by the definitions of the words "lift" and "drag"). So, in this case, lift means the two parachutes are pulling directly away from each other.

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Why did AF447 never return to normal law?
Air France Flight 447 degraded from normal law to alternate-2B law when its pitot tubes were temporarily filled with ice crystals, resulting in a loss of airspeed data.  As a consequence of being in alternate-2B law, most of the aircraft's flight envelope protections were lost, allowing the first officer to stall the aircraft with his counterproductive control inputs, causing the aircraft to experience unplanned high-speed hydrobraking.
However, according to the BEA report on the crash, after only about a minute, the pitot tubes had unfrozen, and all airspeed data was once again valid.  At this point, the aircraft was still climbing, and, although its airspeed was steadily bleeding off, it was still approximately 30 seconds away from stalling (although it was still dangerously close to doing so, and the stall warning horn was sounding); had the aircraft automatically returned to normal law, with all its associated envelope protections, the aircraft would have rapidly recovered itself from the impending stall.
And, yet, despite the clearance of the fault that had caused the aircraft to fall from normal law to alternate-2B law in the first place, it did not transition back into normal law at this point, instead remaining in alternate-2B law all the way up (or down) until impact occurred over three minutes later.1
Why did AF447 remain in alternate law, even after airspeed data from all sources was once again valid?

1: Once the aircraft actually stalled, the airspeed data once again started being invalid (interspersed by periods of validity), but this was due to the aircraft's extreme attack angles during its descent, and would have been avoided had the aircraft not stalled.

If the system detects anomalies for more than about ten seconds, alternate law becomes locked in for the remainder of the flight.

The system detected a change in the median value of the three airspeed sources of more than 30 knots within one second (it actually dropped from 274 to 52 knots within 3 seconds). That started a process where the system monitors the difference for a verification period (about 10 seconds). Alternate Law was triggered, along with limiting the rudder travel limit (which was not annunciated to the crew). The flight control law would have returned to Normal Law if the median speed value was within 50 knots of the original speed prior to the loss, at the end of the verification period. If the speeds remain outside of those parameters, Alternate 2 is locked on for the remainder of the flight, and the rudder travel limit fault is displayed.
emphasis mine

From “Understanding Air France 447” by Bill Palmer

It's clear that it doesn't get automatically reset. Can it be manually reset during flight?

The flight crew have no way to know why it stopped working, or whether it has restarted working correctly. (The fact that they are now "seeing" airspeed data on the instruments doesn't prove that what they are seeing is correct, unless they are at low enough altitude to check by looking out of the window!) So restarting or attempting to restart it simply adds more unknown behaviour into the system -- not a good plan.

If true, that does seem to mean that a crew can be doomed to try to land the plane in alternate law, even if the problem that originally caused the switch was fully diagnosed and fixed hours before. If that is safe (which I suppose it must be) it makes one wonder what having the normal law in the first place provides that is worth the additional cost in conceptual complexity.

@HenningMakholm significant protections in other areas, such as envelope protection et al.  Protections that can be applied safely when the aircrafts systems agree nothing is abnormal with the system itself.

@RogerLipscombe AFAIK they will have to stay in alt law. It's possible that resetting the flight computers might bring back normal law.

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When was Kai Tak permanently closed to cargo service?
Kai Tak Airport in Hong Kong was closed to both passenger and cargo service early in the morning of 6 July 1998, with all flights moving to the brand-new airport at Chek Lap Kok.  However, shortly afterwards, Kai Tak was temporarily reactivated for cargo service (quoting Wikipedia; emphasis added):

Government reports later revealed that Chek Lap Kok airport was not completely ready to be opened to the public despite trial runs held. Water supply and sewers were not installed completely. Telephones were installed, but the lines were not connected. The baggage system did not undergo extensive troubleshooting and passenger baggage as well as cargo, much of which was perishable, were lost. The government decided to temporarily reactivate Kai Tak's cargo terminal to minimise the damage caused by a software bug in the new airport's cargo handling system. During this period, the airport was given temporary ICAO code VHHX.

The article makes no mention of how long this arrangement lasted.
When did Kai Tak close as a cargo airport for the second and final time?

The cargo terminal was closed for good by 24th August, 1998.
First Anniversary of Hong Kong SAR: Infrastructure Development

Air cargo handling was more seriously affected by problems with the automated handling system at the new 'Super Terminal 1' operated by Hong Kong Air Cargo Terminals Ltd (HACTL). This forced HACTL to re-open its air cargo facility at Kai Tak until the new terminal at Chek Lap Kok - one of the world's biggest - was running smoothly. By August 24, all incoming and outgoing air cargo was being handled at HACTL's new Super Terminal 1.

So why did it need its own ICAO code, if only the ground facilities were reopened, and not the airport itself?

@Sean Probably the easiest way to deal with a multitude of cargo handling and routing computer systems.

@Sean The airport itself was reopened, but only to cargo flights. I operated into and out of there several times during the reopening on 747 freighter flights. Thus, for flight planning and ATC purposes, the airport needed its own code. Actually, that period was delightful, with no pax flights going into the airport, there were no delays, either in the air or on the ground, and the normally crowded ramps had plenty of room.


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Do any airports have runways or taxiways that cross active rail lines at grade?
Gibraltar has a runway which crosses an active road at grade (which, due to the peninsula’s geography and the resulting constraints on the airport’s location, happens to be the main road connecting Spain and Gibraltar, thus bringing traffic between the two to a halt whenever the runway is in use), which got me wondering: are there any airports with runways (or, for that matter, taxiways) which have grade crossings with active railroad lines?

There's a question I didn't know I wanted an answer to :D

There's at least one more.

@Harper -- if you're referring to the tracks across twy V at KPMD, then those have been OOS for a while (the frog's gone, and there does not appear to be proper gating in the boundary fence where they cross either)

What do you mean by "grade"? In geographical terms I understood it as short for "gradient" i.e. a slope.

"At grade" is a mainly US expression meaning "at rail height". What Brits call a "level crossing", Americans call a "grade crossing", and in British and American rail terminology, "grade separation" is a method of aligning a junction of two or more surface transport axes at different heights (grades) so that they will not disrupt the traffic flow on other transit routes when they cross each other.

There is another place too, Manakara East Madagascar. Both train and airport are still active.

Welcome to the site!

Also apparently the only remaining place anywhere in the world where an active runway or taxiway crosses an active rail line (as the tracks at Peshawar and Gisborne are out of service, those at Wynyard no longer cross the runway and have since themselves been taken out of service, and, at Filton, both the rail line and the airport are now closed).  Great find!

There is at least one:
In Gisborne, New Zealand, there is a freight rail line which crosses the south end of runway 14/32 at Gisborne Airport (GIS). It appears to still be an active line for freight (logging) haulage, as well as occasional passenger excursions.

Image source: Google Maps, plus own annotation.
This article has some additional pictures and info as well.

Unusual rail line, it has something that looks like a T-junction with a road (see left of photo) :)

The line to Gisborne was mothballed in 2012 after erosion damage rendered it unusable. It's since been reopened for logging traffic as far as Wairoa, but the section crossing the runway at Gisborne remains out of service.

If you look carefully the road is to the north of the rail line, and crosses just south of that t-junction.

@james if you go to Google maps and zoom in to street view, you'll see that it's an actual grade crossing with Aerodrome Rd. not a t-junction. Trains tend to have issues with 90° turns...

Nice find, but the portion of that rail line that crosses the runway has been abandoned, and my question specified active rail lines...

There’s at least another one (not an active  crossing anymore though):

Wynyard Airport, on Tasmania's north-western coast, was quite unusual in that it was one of the few airports in the world to have a railway crossing on a runway.

See link.
Edit: Further down my favourite search engine‘s results, there’s evidence that very question has been discussed elsewhere.

Their is a lightly used freight line crossing the runway at Filton airport, Bristol, UK. Not sure if Filton is still in use as Airbus industries no longer fly their Beluga Airbus from there. As a train driver, i worked freight locos across the branch line. We had  a signal either side of the runway interlocked with a signal cabin.

Filton airport's runway seems to be closed for now...and it also appears the rail ROW that crossed the runway no longer has tracks on it

@UnrecognizedFallingObject    Hi thanks . Yes, its many years since i worked in that area? and the factory the line served had been out of use for a few years. We just used to reverse a loco there. As for the airport, did wonder as Airbus moved away and did here it was to be used for housing . Was not sure if general aviation still used it.


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Is it best to use a thick airfoil or an undercambered airfoil for slow speed flight?
The more the thickness,the more the frontal resistance,hence the more the drag a thick airfoil will produce.
Under cambered can help increase lift without increasing the airfoil thickness , therefore not creating as much increase in resistance or drag . ..which is more plausible for a slow ultralight,a thick airfoil or an under cambered airfoil?

Source: https://www.flitetest.com/articles/beginner-series-basic-aerodynamics

Under cambered is not a common expression. Please clarify!

Ok..airfoil with inward curving shape of its undersurface @Peter Kämpf.

There's no difference in crossection area for undercambered and cambered airfoil assuming the undercambered one was created by "carving out" the cambered one. It's not dependent exactly on thickness

Frontal area* crossectional area changes, but frontal projection area is what matters

First of all, the thickness-related drag increase is small, especially for airfoils below 15% of thickness. Thickness by itself mainly determines structural efficiency and wing volume and is chosen on those merits. A very common choice for GA planes is 15% - 16% at the wing root tapered to 10% - 12% at the wing tip.
Next, much depends on the wing's bracing. A pure cantilever wing will be heavy but produce very little drag, so it is the obvious choice for faster aircraft; however, bracing the wing will lower wing mass and, therefore, induced drag. For slow airplanes, bracing the wing helps to reduce drag at low speed. But how much bracing is the best?
Clearly, early designs used too thin airfoils and went overboard with the bracing. Look at the picture of a replica of the Etrich Taube, a very popular plane of the pre-WW I period.

Etrich Taube in flight. Note the truss below the wing and the many wires keeping it in shape (picture source).
Next, many low speed aircraft used two braces, one forward and one aft, and an airfoil of between 12% and 15% because this helps them to get most lift from a given area. Note that all use high-lift devices: Slats and slotted flaps are a must:

Westland Lysander (top, source) and Fieserer 156 "Storch" (bottom, source). Note the very similar wing bracing and flat-bottom airfoil.
Multi-element airfoils are complex, so maybe it will be best to look at gliders and motorgliders for inspiration - or even human-powered aircraft. Also, the Reynolds number, which is determined by the size and speed of the aircraft, needs to be considered. As a very rough rule of thumb: If you only want to fly slowly and operate at a Reynolds number below 1 million, use a highly-cambered airfoil like the Daedalus sequence (DAE11 at the root, DAE21 mid-span and DAE31 at the tip). For more flexibility and Reynolds numbers above 1 million consider a camber flap and a glider-type airfoil.

I have an amazing book, called The Miracle of Flight by Stephen Dalton, which describes aerodynamics and flight mechanics by moving up the Re scale through the natural world to the man-made one.  Wings start out super thin, more or less single surface (bugs, with Re down in the thousands or less, for whom the air is like motor oil), get thicker and thicker as Re goes up (birds, early a/c, conventional a/c wings), then get thinner again when the speeds get high.

@JohnK: Yes, such a scale is very instructive. The smallest flying insects do away with conventional wings and have something resembling brushes for creating lift.

Informative!.....+1k for answering a question no one was willing to answer... @Peter Kämpf


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What airfoil is used on the Lazair ultralight?

This is the airfoil of the famous Lazair ultralight. What is the name of this airfoil?

Famous? I'd not heard of it before this.  Ah, I see why:  "sold in kit form between 1979 and 1984", so production stopped 10 years before I started flying.

That looks close but I think there is too much camber in it as depicted above, and that is only the root airfoil.  There are significant changes along the span.
I used to jokingly call it my 'Lie Back' airfoil because I usually design things at night in bed :)
At some point I hope to get a 3D CAD model published of the whole Lazair series of aircraft but I can't promise when.
The Lazair is to be featured on a Canadian stamp this year and there is a Lazair in the Smithsonian :)
Dale Kramer
PS.  Peter Corley was killed in the Toucan of his own design and I never flew any aircraft with Peter hanging on my waist.

Welcome to Stack Exchange, Dale, and thank you for your answer! I hope you stick around!

Dale on Stack exchange?!?!.....wow,S.E keeps getting better.Welcome Sir.

It's designer Dale Kramer's own home brew airfoil he developed mostly out of intuition and educated guessing. I don't know if he gave it a name.  I visited their kit factory and nearly bought a Lazair in 1979.
From Lazairinfo.com:

Airfoil: Custom Lazair airfoil, reflexed top and bottom (said to be eyeballed by Dale Kramer)

The reason why am asking is 'cos the airfoil looks thick and the first series of lazair flew with 11hp meaning this airfoil is really efficient....

What was more impressive is I personally watched Dale take off with his business partner, Peter Corely, (later killed demoing at an airshow) hanging on behind the rear down tubes with his legs around Dale's waist.  The airplane wouldn't climb above about 30 feet but they completed a circuit of the field and plopped it down.  Peter was a reckless sort.

I think a downside to that airfoil is it was draggy enough to limit the airplane's L/D to about 10 which I think is low for a relatively clean design with a high aspect ratio.  I would've expected an L/D closer to 14 or 15.

Okay,I guess the airfoil wasn't as efficient as I thought... Wow u saw Dale and Peter demoing at an airshow...that means you're Canadian...(cool).....anyway...thank you for enlightening me on Lazairs airfoil.@John K

It was at the field near Welland, Ontario they flew from.  The factory was in town right beside the Welland Canal. Dale lives in NY State now.


text:
Does angle of rotation during takeoff affect the g-force?

(Original)
When an airplane banks 60° during row, 2 g of force is induced. When an airplane pitches 60° during takeoff, is 2 g induced on the airplane?
Is the angle of rotation during takeoff related to the amount of g-force made during takeoff?

That is not  60° of pitch up. Not even close. In the US, more than 30° requires everyone to have parachutes except during some training maneuvers towards a certificate. I would bet other countries flying similar aircraft have similar regulations.  US FAR 91.307  (c) Unless each occupant of the aircraft is wearing an approved parachute, no pilot of a civil aircraft carrying any person (other than a crewmember) may execute any intentional maneuver that exceeds—
(1) A bank of 60 degrees relative to the horizon; or
(2) A nose-up or nose-down attitude of 30 degrees relative to the horizon.

How many Gs do you experience when you are walking on a 60 degree slope?

.....good point!

Just to give you an idea, here's a very crudely done superimposition of a 60°-up pitch on the image in your question: https://i.sstatic.net/JjTZG.jpg (If anyone wants to use this in an answer, go right ahead.)

The increase in g-force in a banked turn is due to centrifugal force. That's a completely different situation than the g-forces during takeoff.
The forces during take off will be due to acceleration from thrust and, at rotation, an upward acceleration due to lift (and part of the thrust). The pitch angle doesn't have a direct relationship to g-force as the roll angle has in a banked turn. During climb the pitch angle can be as high as 15°, but once you've established a steady climb and a steady airspeed the g-forces are just the 1g of gravity.

No. The angle of attack is related to the force, to a degree.
The difference in this case is the angle between the direction the nose is pointing and the angle the aircraft is actually flying. Consider the second of the two diagrams; the aircraft's nose is pointed up at something like 15 degrees, but at that very instant it is still rolling down the runway, so its direction is flat. The angle between the two is the important one in this case. To further confuse things, the wings are often connected to the fuselage so they have some inherent angle, usually a few degrees positive, so in this case the angle of attack, or AoA, could be anywhere between 10 and 20.
Now that's half of it. The other half is the actual force that results, which is the g force you feel. That force, the lift, depends on the AoA, the speed, and the design of the wing. For any given single wing design, you can make a chart like this:
https://en.wikipedia.org/wiki/Airfoil#/media/File:Lift_drag_graph.JPG
I cannot embed this for some reason. Anyway, the image shows the lift coefficient vs. AoA, which you can then multiply through the formula found on that page to calculate the lift. Add gravity, and there's your g.

"I cannot embed this for some reason" Wikipedia prevents it. you have to save the image on your pc and then upload it through the interface here


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How to determine the compressive force in the spars of a strutted wing?
How does one calculate the compressive force that the inner section of a strutted or braced wing (from the strut attach point to the wing root) experiences?
I know how to calculate the tension in the struts (or flying wires), which is simply
$$ \mathrm{Tension} = \cfrac{\mathrm{Lift}}{\sin \theta} $$
but I don't know to calculate the compressive force that a strutted or braced wing experiences.

Are you sure about that tension equation? I don't think it is correct, as it disregards the cantilevered wing. For $\theta$ approaching $\pi/2$ it would imply that the flying wire would take on near all the lift, which is patently untrue.

Are you really worried about the compressive force on the lower area? I would rather be more worried about the stretching force on the upper area.

@user40476 buckling can kill a beam in an instant.

@AEhere, correct,  but the split or the crack starts on the stretched surface

Good thing you included the image, it's much clearer now. Although what's the text left of "strut"?

"Lift".........

@DavidTeahay I mean below the arrow pointing down.... Unless you have a lift force pointing down?

Oh....it's "wing strut"@Sanchises

@David Teahay in your diagram the vector of the strut must be pointing along its length, then broken into lift resistance and compressive vectors (down and in).

Yeah the formula is correct@AEhere check This out www.bowersflybaby.com/safety/bracing.htm

These pictures hopefully will improve the question and serve to validate Sanchises answer.
If I could find a flying wire to take on near all the lift, I would patent it!

Note that I purposefully did not express the compressive forces as a function of lift, but as a function of force in the strut. There can be a coincidental geometry where the vertical force exerted by the strut is equal to lift, but it's definitely not true in general.

(also, just placing the strut exactly under the center of lift is hardly patentable, and a waste of bending strength of the wing...)

@Sanchises Hey, I can't believe they handed me the check mark either (thanks to you).  After reviewing this design I can see why they went cantilever.  Would love to see a flitched wooden spar and plywood stressed skinned wing.  Now that would strong.

It's very easy. Consider that the point at which the strut is attached does not accelerate, i.e., the forces in all directions exactly even out.
The force in the spanwise direction exerted by the strut is
$$F_{strut}^{spanwise}=\cos\theta\cdot F_{strut}$$
This force must be balanced by the wing in compression, so the above expression is also valid for the amount of compression on the wing.
This assumes the strut only transfers longitudinal forces, while in reality it may have some bending stiffness. Also, I'm not sure where you got your equation for the tension in the strut, but it's not necessarily true (there's a lot more structural members exerting a vertical force on the wing, so the force- and moment balance is not as simple).

For dimensioning purposes, consider the intersection points to exert no moments and to behave as hinges.

Force equilibrium in point 1:

$F_{13} \cdot sinψ = ½L => F_{13} = \frac{L}{2sinψ}$
$F_{12} = F_{13} \cdot cosψ = \frac{L}{2tanψ}$

Yes the forces create stretch. Strut 1-3 is the longest strut with the highest force, and will stretch more than the other members. The triangle will be slightly deformed, but because of the hinge modelling all of the members will still be loaded by compression/tension forces only.

Would it be correct to start with the lift and tension vectors at point 1 only, then decompose the tension vector of the strut to vertical (opposing lift) and horizontal (compressing inner wing spar)?

To balance forces F12 could be coming from the other strutted wing!

Analytically, using beam theories, like Timoshenko or Bernoulli, maybe, see below.
Numerically, via FEM.

This is a pretty classic exam question involving a statically indeterminate (or over-constrained) system. To solve it you will need to solve the beam equations with the correct boundary conditions, which may or may not be possible (I do not recall at present whether the "cantilever and wire" has an analytical solution, I'll update this later).
Alternatively you can obtain an approximate solution by relaxing your boundary conditions, for example exchanging the cantilever for a point support with a torsional spring of suitable stiffness.

An anonymous comment pointed out that strut braced wings are almost invariably pin-jointed structures to maximise structural efficiency, the system is statically determinate. In this case the structure is analytically solvable without the need to muck around with boundary conditions and beam equations:
Reactions and internal loads for the 2D free body shown can be resolved by basic statics. The strut is a two force member, experiencing axial loads only. The inboard portion of the spar which experiences compressive loads in reacting the spanwise component of strut tensile load is usually idealised as a beam-column.

It most certainly has an analytic solution as a Bernoulli beam (probably Timoshenko too but that seems overkill for such a slender member as a wing)


text:
What's the name of this light airplane?
The propeller of this light airplane almost looks like a triangle, so I'm interested in knowing its performance but I need help in identifying this plane because I don't even know her name.

I notice the word Hornet painted on the engine cowling.

It looks very concerned...

@Harper: It looks like the love child of Robotnik and Gru.

Looks like the "Homebuilt Hornet, one-off wonder plane" on the cover of the March edition of the Australian Sport Pilot Magazine.

The article can be found on pages 34-37.

The aircraft is a Hornet, built as a one-off by Australian Colin Jamieson. The fuselage was made from two canoes, and it's powered by a 80hp Jabiru engine.
It featured in the March edition of Australian Sport Pilot, where you can see more pictures and read something about it's history.

Two canoes, but no floats???

Wouldn't be the first case of airplanes mixing with canoes

Jabiru in Australia seems to be engine manufacturer. They also supply propellers.
https://jabiru.net.au/propellers/
The prop pictured doesn't too much like the 2200 Wooden Laminate they offer for the 80 HP 2200 Aero Engine
https://jabiru.net.au/wp-content/uploads/2018/05/2200-Aero-Engine-Flyer.compressed.pdf
To my eye, it doesn't look triangular.

The prop blade on one side is quite a different angle than the prop blade on the other side.  It sort of suggests triangles.  Interesting aesthetic choice...

The keading edge on both blades is forward on the spinner. I get the impression you have not seen a fixed prop in person. You should visit your local small airport and ask for a tour, to look at the planes up close.

Oh I actually thought the prop was tapered to reduce induce drag and increase efficiency #CrossRoads


text:
100% Homebuilt Airplane

THIS IS JUST A SIMULATION OF THE INTENDED AILERON THAT I'LL BUILD AND PUT ON MY HOMEMEADE PLANE.(I scrampled all the materials I could find in my backyard).
Do you find any abnormality in this aileron in relation to the aileron on real planes('cos I have never really seen the aileron setup of a real plane)

What country are you in?

Looks like you have the basics of the wing mounted control horn down.  Maybe change the aileron connections (both ends of the threaded rod) to a ball & socket setup so there is no 'slop' in the control from a rod in a hole; don't want any fluttering from loose connections.

Your control link to the aileron will fail in compression from buckling long before the expected flight loads are reached. Try to use tubes, not rods.

Okay thank you so much  Peter @PeterKampf

For a non-working prototype it doesn't look too bad - you have a bell crank connected to a control arm that's attached to the aileron.
However, the devil is in the details and messing up a detail can kill you.

You will want to use acceptable materials and construction techniques (See AC 43.13).
You need to ensure the bell crank is the right size so the control forces are correct (neither too big or too small).
You need to ensure the aileron is the right size and shape and travels the correct amount.
You need to ensure your hinges are of sufficient quality (hardware store stuff will break and can kill you) and are attached to the wing safely (losing an aileron can kill you)
You need to ensure your aileron isn't subject to flutter (which can kill you)

If you haven't already, contact the EAA and get as heavily involved as possible.  They have an incredible amount of information available about how to safely design and build an airplane from the runway up.

Can any of that kill you?

Okay Thanks A lot @Dan Pichelman

Not sure what specific feedback you are looking for here, but if the question is "will this work?" or "is this a good idea?" Then the answer is probably not. If you never built a plane before and have never even seen the design before, just making it up as you go is not a good idea. If this is a toy remote control plane, then you could get away with it. But if you intend for a person to fly in this, then you do not want to do this. For your first plane buy a kit, or at least get plans/blueprints for a proven design. Once you know how these things work, then maybe start improvising a little by modifying existing designs. Sorry to rain on your parade but I think you are taking risks that you do not need to take.

Okay,thanks Dan

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
why lift is greater at wing root
Is lift greater at the wing root of an horizontal wing,just like it's greater on a tapered wing?

Is lift greater at the wing root of an horizontal wing,just like it's greater on a tapered wing

Well this is sort of definitional.
Generally speaking the idea of any sort of taper or shaping of the wing like the examples you posted above is to deliberately reduce the lift at the tips in order to reduce induced drag. In that case, no, the rectangular wing would be more even across the span - although there's all sorts of other effects that would likely come into play that would adjust that to some degree.
But really what you're asking about is the lift per span. If you really mean "is there more lift at the root" then the answer is "absolutely every time" for the simple reason that the lift force at the root is the lift force of the entire wing, whereas at the tip it's the force of only the tip. That's why the spars get thicker as you move in toward the root.


text:
Why are the VHF and UHF airbands directly adjacent to frequency bands used by vital radionavigation aids?
Of the three main frequency ranges used by aircraft for radio communications (HF, VHF, and UHF), two (VHF and UHF) have their aircraft-radio-communications frequencies clumped together into a contiguous (or almost contiguous) airband1 (117.975-137 MHz for VHF, and 225-328.6 MHz and 335.4-399.9 MHz for UHF2).
Interestingly, and somewhat worryingly, each of the VHF and UHF airbands is immediately adjacent to a band of frequencies used by vital radionavigation aids:

The VHF airband (117.975-137 MHz) lies immediately above the 108-117.975-MHz band used by VOR and localiser transmissions.3
The two UHF airbands (225-328.6 MHz and 335.4-399.9 MHz) are separated by the glideslope-transmitter band (328.6-335.4 MHz).

This raises the possibility that a malfunctioning (or even just poorly-tuned) VHF radio could cause interference for VOR or localiser signals if it went even slightly out-of-band, or (much worse) that a mistuned or malfunctioning UHF radio could end up stepping on somebody’s glideslope.
Given the navaid-interference potential thereby caused by this adjacency of radiocommunications and radionavigation bands, why do both the VHF and UHF airbands directly border frequency bands used by vital navaids, and how are out-of-band VHF and UHF radio transmissions prevented from thereby causing interference with these navaids?

1: The HF frequencies used for aeronautical radio communications, in contrast, are split into multiple discrete bands spread out throughout the entire HF range.  This is because the main attraction of HF is its ability to transmit and receive signals far beyond line-of-sight range (potentially even enabling an aircraft to talk to someone at the aircraft’s antipode, on the opposite side of the planet); which HF frequencies work best for this depends on the current state of the earth’s ionosphere, which varies considerably due to things such as solar activity, variations in the Earth’s magnetic field, recent high-altitude nuclear explosions, supernovae, witchcraft, etc., so the aeronautical HF bands are scattered throughout all HF in order to ensure that there should be at least one useable band no matter what (the frequency bands used for shortwave radio broadcasting are likewise scattered throughout most of the HF range [although, surprisingly, not the lower end], for the same reason).  In any case, the HF range has no radionavigation bands of any sort whatsoever, making it not a concern for the purposes of this question.
2: Which, if you want to be pedantic, places a good portion of the UHF airband in what is actually the top end of the VHF range.
3: And the 108-117.975-MHz radionavigation band is, in turn, immediately underlain by the FM broadcast band (88-108 MHz), but, as there are fewer FM radio stations than there are VHF-radio-equipped aircraft, and they are bigger and easier to spank if they get out-of-band, this is less of a concern from the interference-with-navaids perspective.

Did you mean to say contiguous in place of continuous?  Because one could say the frequencies border one another, although it is generally used as a geographical term.

@MichaelHall: Yes, I meant to say "contiguous", to indicate that the VHF and UHF airbands aren't split up and scattered apart from each other like the HF bands are.

The most obvious reason is that the ITU allocated the VHF and UHF bands for aviation purposes generally, and then aviation authorities had to split those limited bands into adjacent comm and nav sub-bands.
If aviation had gotten separate ranges for nav and comm, then that would double the risk of interference from adjacent non-aviation users, plus it would have made designing radios and sharing antennae more difficult.
So, we got the lesser of two evils.


text:
Why were early AFRP A300/A310 rudders prone to delaminating?
Reading the TSB report about that time an A310's rudder flew the coop, I came across this piece of background information (section 1.12.9.1, History of Earlier Design Aramid Fibre-Reinforced Plastic Rudders):

In the earlier design of the rudder, GFRP [glass-fibre-reinforced plastic] was used as the bridging layer between honeycomb and CFRP [carbon-fibre-reinforced plastic] only in the reinforced region around the hydraulic actuators. Elsewhere, AFRP [aramid-fibre-reinforced plastic] was used. The AFRP system resulted in poor bond strength of the interior skin. Those rudders experienced large in-service disbonds of the inner skins.  [...]

What made A300/A310 rudders using AFRP so prone to the rudder skin delaminating from the underlying structual framework?

You'd have to find someone with access to the original Airbus failure analysis to know the details, but in general it's more difficult to get good bonds with Kevlar laminates compared to graphite or glass (something to do with helpful reactive compounds on the surface of glass and graphite fibres that Kevlar lacks), and special surface treatments and epoxies are required.
I'll hazard an educated guess that Airbus engineering at the time may not have had a lot of experience with Kevlar composites and didn't appreciate the bonding issues sufficiently, and it didn't show up in testing and took the stresses of service operation to uncover it.
Nothing new there as such screw ups go... on the CRJ200, the floors were carbon honeycomb set on floor beams of aluminum.   Somebody seemed to have missed their galvanic scale class in university and didn't realize that carbon and aluminum don't like to live side by side, and areas of the floor see significant moisture from people spilling stuff, rain coming in the doors, humidity, etc.  The company ended up replacing the floor beams on the first couple hundred airplanes with titanium ones.


text:
What prevents the use of a multi-segment ILS for non-straight approaches?
An ILS, consisting of a localiser beam to provide lateral guidance (which can also be used on its own for a non-precision approach) and a glideslope beam to provide vertical guidance, is (currently) indispensable for precision approaches in IMC, but comes with a few disadvantages.
Chief among those is the fact that an ILS only supports approaches that are ramrod-straight all the way in from the outer marker, when such an approach path is often impossible or undesirable...

...sometimes because something too solid to fly through is in the way (for instance, the infamous approach to runway 13 at Kai Tak, which, due to an inconveniently-placed mountain, necessitated coming in at a large angle to the runway and then making a sharp right turn at very low altitude at almost literally the last moment; an instrument guidance system - basically an ILS without the “landing” part - was added in the 1970s to provide precision guidance for the part of the approach before the turn, but the turn itself and the final approach segment still had to be hand-flown visually, an exceptionally difficult task even in good weather)...
...and sometimes because someone else is using part of the airspace in question (for instance, the four major airports in the New York area [JFK, la Guardia, Newark, and Teterboro] have numerous intersecting approach paths, which, as the approaches can’t be bent or segmented to keep out of each others’ way, frequently forces la Guardia and Teterboro to land aircraft on runways with strong crosswinds [because the ILS approach paths for their more optimal runways would risk causing MACs with aircraft on ILS approaches into JFK and/or Newark]; on the other side of the continent, the approach paths coming into LAX from the east pass near or over Ontario, which has caused quite a number of near misses in the vicinity of the latter airport).

It doesn’t seem, conceptually, like it should be too hard to break up an ILS approach into two or more segments, each with its own localiser and glideslope, and with the beams from the pre- and post-bend segments intersecting at the bend in the approach path.  As most aircraft are unable to turn on a dime, they would need to start turning a bit before the bend in the approach, but this could be easily handled by having another instrumental aid (for instance, a third localiser) indicate when to start turning; if the bend in the approach were sharp enough for the aircraft to have trouble locking onto the post-bend beams, another localiser and glideslope, with their beams tangent to the midpoint of the turn, could be used to assist the aircraft round the bend.
All of this would also work for segmented localiser approaches, with the added advantage of being easier to implement (no need for the multiple glideslope antennae, just the localiser ones).
Here be an illustration of what I’ve got in mind:

Why aren’t segmented ILS and localiser approaches used in practice?

You might be interested in the MLS (microwave landing system) which has the capability of a segmented approach due to a much wider beam (https://en.wikipedia.org/wiki/Microwave_landing_system)

Innsbruck (LOWI) sort of does this

See here, pages 5-23, 5-24.  Things have advanced well beyond ILS for that kind of approach.
https://whispertrack.com/pdf/faa_handbook.pdf

REQUIRED NAVIGATION PERFORMANCE
  The operational advantages of RNP include accuracy
  and integrity monitoring, which provide more precision and lower minimums than conventional RNAV.
  RNP DAs can be as low as 250 feet with visibilities as
  low as 3/4 SM. Besides lower minimums, the benefits
  of RNP include improved obstacle clearance limits, as
  well as reduced pilot workload. When RNP-capable
  aircraft fly an accurate, repeatable path, ATC can be
  confident that these aircraft will be at a specific position, thus maximizing safety and increasing capacity
To attain the benefits of RNP approach procedures, a
  key component is curved flight tracks. Constant radius
  turns around a fix are called “radius-to-fix legs,” or RF
  legs. These turns, which are encoded into the navigation database, allow the aircraft to avoid critical areas
  of terrain or conflicting airspace while preserving positional accuracy by maintaining precise, positive course
  guidance along the curved track. The introduction of
  RF legs into the design of terminal RNAV procedures
  results in improved use of airspace and allows procedures to be developed to and from runways that are otherwise limited to traditional linear flight paths or, in
  some cases, not served by an IFR procedure at all.
  Navigation systems with RF capability are a prerequisite to flying a procedure that includes an RF leg. Refer
  to the notes box of the pilot briefing portion of the
  approach chart in figure 5-17.

The Approach in Fig 5-17 has 5 turns left & right!

Even if it were technically possible to have a multisegment ILS approach, the economics just don't make sense.
Each ILS costs millions to install and millions more to keep running properly over its lifetime. You need a lot of traffic to justify that cost. Now multiply that by however many segments you need, and then consider whether an airport that hard to get into is going to have enough traffic to justify that enormous cost.
OTOH, RNAV approaches can have any number of waypoints along an arbitrary path; they can even have curved segments between waypoints. There is no ground equipment that needs to be installed or maintained, just the one-time cost to develop the procedure, so it's orders of magnitude cheaper despite being more capable.

As mentioned in all the answers so far, it's no longer really necessary to take the mulit-segement ILS approach methodology. However, cost in an area like NYC with it's 4 major airports with conflicting ILS approaches would have been a factor, but one that probably could have been accommodated if there weren't other technical/regulatory reasons not to do so. I'm sure a few million a year to increase bad weather throughput at 4 airports would have been a worthwhile investment.

@FreeMan: Kai Tak would probably also have been a worthwhile investment (given that it was the third-busiest airport in the world in its later years) had it not been a dead airport walking.


text:
Why would a pilot's armrest be a no-go item?
From the end of issue #216 (June 1997) of Callback:

Another First Officer also learned too late the importance of consulting the MEL before take-off.

Inbound equipment arrived late. About 5 minutes before pushback time, I discovered that my right armrest was stuck in the UP position. I attempted to free it, but no luck. I contacted maintenance and asked them to bring something to lubricate the mechanism. A mechanic did so, but to no avail. We figured we could just go with it in the UP position. It did not occur to us to look it up in the MEL, as it did not seem to be a safety-of-flight item.
Upon our arrival, we were told that the armrest is a no-go item. The continuing flight was cancelled due to this fact, since no spare seat or replacement part was immediately available. The Captain and I were both amazed that something as simple and innocuous as an armrest would be considered a no-go item. In the future, I will check the MEL for any item, no matter how seemingly insignificant.

Why would a pilot's armrest stuck in the up position be a danger serious enough to require grounding the aircraft?  One would think, like the aforequoted pilot did, that it would be, at worst, a minor inconvenience, and certainly not a safety-of-flight issue...

If say it was a FBW Airbus with side sticks, the side armrest may have been a critical item for dispatch, because the ability to rest your arm on it so you can control the stick with your wrist was important, and Airbus would be unable to get MEL relief.  Does it say anywhere what the type was?

@JohnK I Googled "mel pilot armrest" and the first result shows " In addition, in turbulent conditions, the armrest stabilizes the pilot's...."

This is ACN 314861, and it happened in a B757-200 in the year 1995. The report notes that "there are some crewpersons that use them for leverage when needed while other crewpersons never use the armrests."

When I was flying RJs I always used the arm rests because it permits fine control with your wrists.

Perhaps it was just an oversight on the part of the creators of the minimum equipment list.
As I understand it, minimum equipment lists generally provide a list of those items which are permitted be inoperable. So if any piece of equipment is inoperable, and it's not on the list, that automatically means you're not allowed to fly.
(Going by the name, you'd probably expect a minimum equipment list to be, you know, a list of the minimum required equipment. But for one reason or another, it's not.)
So, in all likelihood, nobody thought to add armrests to the minimum equipment list. As a result, flying with an inoperable armrest was automatically prohibited.
However, things have since been adjusted: the FAA has added the armrest to the master minimum equipment list for the Boeing 757. So, it is now legal to fly your 757 with a stuck armrest, as long as it is stuck in the "up" position.

Are you sure about your understanding of the MEL? See: https://aviation.stackexchange.com/a/12071/23223

Tanner has it correct.  What is not covered under the MMEL grounds the airplane if broken. The OEM will continuously expand the MMEL over the life of the program because it's critical to getting the dispatch reliability to target, but starting out, there will be all sorts of items not covered.

...okay, then, why does having the armrest stuck down ground the aircraft, but not if it's stuck up?

Usually anything that impedes a rapid exit is not allowed.

@JohnK From the AOPA link in the answer I mentioned: "An MEL is a list of equipment that must be installed and operable for the aircraft to be considered airworthy" is what was confusing me. It does make more sense to default to no-go if an item is not explicitly allowed to be inop. Thanks for clarifying.

You'll also notice that the vast majority of items covered in the MMEL are elements in redundant systems that allow continued function but without or degraded redundancy.  It will be based on a risk analysis of the possible follow on effect of a subsequent failure, with a risk exposure window, within which the risk of bad news is acceptable.  Typically 10 days, or for more criticality, 3 days. There is often a mitigation action that has to be done in concert, like a daily ops test of a system that is normally checked at A check (4-600 hrs), that was required to get an acceptable risk profile.


text:
Why do light taildraggers swirl uncontrollably on runways in a simulator?
When a pilot chooses to run at a speed way above its takeoff speed on the runway in a simulator without taking off, the plane begins to skid and spins 360 uncontrollably around the yaw axis, what is the cause?

Simulators, especially home ones, are generally unrealistic when an airplane is in contact with the ground.

Yes....thanks @ymb

Ok no problem..

A taildragger is more or less a shopping cart being pushed backwards, or a car driving fast in reverse.  It's dynamically unstable when rolling and wants very badly to switch ends, requiring constant input to the steering.

the prop wash from the propellers swirls around the body in the same rotation direction of the propellers and hits the rudder making it deflect a bit. for example if the propellers rotate clockwise, rudder deflect to the right and pulls the nose to the right which has to be countered by pilot's applying a bit left rudder pedal to neutralize the motion. if not counteracted, the directional deflection in the take off roll on the runway can send the plane off runway and spinning around itself in a tight radius. There is no such phenomenon in multi-engine propeller aircrafts since the rudder stays out of the propwash.


text:
Is there any alternative to isolating the vibration of an ultralight engine other than using engine mounts?
Is there any alternative to isolating the vibration of an ultralight engine other than using engine mounts?

You can prevent engine vibrations from being transmitted to the airframe by motion cancellation techniques. Similar in principle to Active Noise Reduction headsets that generate an inverse pressure wave to cancel sound, motion cancellation generates an inverse displacement of a mass to cancel vibrations.
Sensors determine the vector(s) required, and electronics control the mass actuator(s). These can be added to any engine. Predictable, repetitive vibrations are most successfully treated. Actuators tend to be heavy, so better engine/prop balance and more effective isolators (mounts) are preferred.

As you've noted, engine mounts are used to isolate the vibration of the engine from the airframe.
Another technique is Dynamic Prop Balancing - adding weights or washers to specific places on the propeller or spinner to eliminate the vibrations.
It's the same idea as is used to balance car tires.

Perhaps the choice of the engine helps, flat-six does vibrate less than in-line engines, also Wankel Rotary Combustion Engines have an intrinsic very low level of vibrations.
Some interesting approaches were proposed, as this patent from the extinct Barcelona Based motorcycle maker: 'Sanglas'. They once prepared a working prototype for a single-cylinder, 4-valve, 750 cc engine.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Why does spin recovery involve cutting the throttle?
When recovering from a spin, the first step is generally to cut the throttle:

... Otherwise, to recover from an upright spin, the following generic procedure may be used: Power is first reduced to idle and the ailerons are neutralized. Then, full opposite rudder (that is, against the yaw) is added and held to counteract the spin rotation, and the elevator control is moved briskly forward to reduce the angle of attack below the critical angle. Depending on the airplane and type of spin, the elevator action could be a minimal input before rotation ceases, or in other cases the pilot may have to move the elevator control to its full forward position to effect recovery from the upright spin. Once the rotation has stopped, the rudder must be neutralized and the airplane returned to level flight. This procedure is sometimes called PARE, for Power idle, Ailerons neutral, Rudder opposite the spin and held, and Elevator through neutral. ...  [Wikipedia]

This is extremely counterintuitive; given that another vital step in spin recovery is to apply full down elevator1 to get the nose down, one would expect that the blowback from the engine (especially for tractor-propeller aircraft) would aid in recovery by striking the underside2 of the deflected elevator, and, thereby, pushing the tail up (and the nose down), making it seem, at first glance, that it would be best to firewall the throttle in order to get the tail up and the nose down as quickly as possible.
In addition, even without the contribution from the elevator, applying full throttle would:

drag the aircraft forwards through the air, increasing the forward component of its motion and decreasing the angle of attack seen by all the various parts of the aircraft;
for tractor-propeller aircraft, blow air at high speed backwards over the wings, dramatically lowering the local angle of attack felt by the wings.

Both of these effects would tend to destall the aircraft and transform the spin into a boring old trivial-to-recover-from spiral dive.
So why do spin-recovery procedures for most aircraft generally call for cutting the throttle, rather than firewalling it?

1: Or, if spinning while inverted, full up elevator.
2: Replace "underside" with "upper side" if spinning inverted.

PARE is just a generality, it's not a universal procedure for all aircraft.

Applying engine power can indeed help to end a spin. But the added thrust will make an overspeed in the ensuing spin recovery much more likely. Also, applying asymmetric thrust on the wrong side will flatten and stabilize a spin. These are the main reasons why the engine should be idle in spin recoveries.
Remember the Boeing 307? The first passenger airliner with a pressurized cabin and the civilian version of the B-17. It was test-flown by KLM personell on March 18, 1939. It entered a spin after a stall and the rudder became stuck in spin direction. The pilot applied asymmetric power in order to stop the yawing motion and succeeded in doing so, but in the subsequent recovery the aircraft oversped and the outer wings broke off. Here is the official accident report.

Boeing 307 in flight (picture source). Note the small fixed vertical surface which was replaced after the crash with a much bigger one.
Symmetrical thrust can be helpful or adverse for spin recovery, depending on circumstances. NASA TN D-6575 from December 1971 says that

no systematic study of the effects of applying power during a spin

is known and

The effect of applying symmetrical power in a spin is believed to be insignificant. A number of varied observations have been made through the years by many people, and the conclusions regarding power effects on spins range from favorable to adverse. […] In almost all cases, the results were not obtained under controlled conditions. Therefore, the type of spin, the center of gravity, the angle of attack, the spin rate, and the line of thrust with respect to the center of gravity were not identified.

Therefore, a general recommendation for applying symmetric thrust for spin recovery cannot be made and only asymmetric thrust has shown to be helpful if applied correctly:

the application of thrust had no effect unless the thrust axis was displaced from the center of gravity and thereby produced a moment.
[…]
For asymmetric power for a twin-engine configuration with the engines mounted on the wings, power from only one engine can produce a large asymmetric yawing moment, which will be favorable or adverse to the spin and recovery, depending on the direction of the moment. Both model and full-scale spin-test results of multiengine airplane designs have shown that power on the outboard engine (e.g., the right engine in a left
spin) can create a large prospin yawing moment, which can cause a flatter and faster spin. On the other hand, power on the inboard engine can create an antispin moment to aid spin recovery. Normally, the manipulation of thrust can be confusing and disastrous if the power is applied to the wrong engine. Therefore, unless asymmetric power is necessary to aid recovery, it is generally recommended that for a multiengine airplane, the throttle be retarded to the idle position on all engines during a spin.

It should also be mentioned that the extreme angle of attack at the inboard engine will produce an extreme sideways displacement of the thrust vector on a propeller or uneven flow in a jet intake. In both cases such a flow condition was most likely not anticipated during design and could result in the loss of the propeller rsp. a compressor stall in the jet engine if full thrust is applied.
While I do not know of a propeller having been lost in a spin, during the flight test of the Dornier 328 an extreme sideslip did indeed overload the left propeller, parts of which tore a massive hole into the fuselage.

Several issues:
Gyro precession induces pitch effects that may help or hinder depending on the direction of rotation
P factor, which may help or hinder depending on the direction of rotation.
Propeller wash may tend to help unstall the wing root a bit, but the rotational force is coming from the unstalled wing driving forward and the stalled wing at the other end holding back, so blasting air over the wing roots may not have much effect.
The axis of rotation is somewhere around the inboard end of the stalled wing, not in the center of the fuselage, so that the thrust, instead of pulling the airplane straight, is just applying a torque that assists the unstalled wing in the rotation.  Adding power may just speed up the rotation.
Lots of airplanes have different spin characteristics power on and power on, and left to right, especially with power on, and it's better to just remove the propeller's influence completely to allow a consistent technique to be used.
When pilots get into spins and the normal inputs don't help, that's when they start to experiment with different control inputs and power.  Sometimes works and sometimes doesn't.
The vast majority of light aircraft recover by themselves if you just let go of everything within the 1st turn or so.  Even airplanes that are not certified to spin will generally auto-recover unless they are held in the spin for an extended period.

Adding power can tend to make the spin go flat in some aircraft.
Yet in some cases, adding power can aid spin recovery, especially in a flat spin.
I've owned a radio-controlled model airplane that would enter a really nice flat spin, with the fuselage nearly horizontal and a rather substantial yaw rotation rate.  In fact, once I figured out the best technique to enter the flat spin (which involved carrying about half power into the entry), I could get consistent entries to flat spins at CG locations that were too far forward to consistently enter a nose-down spin.
Once established in a flat spin, the plane would consistently recover if I gave it lots of power and kept the controls neutralized.  On the other hand, leaving the power off and giving full down elevator and full anti-spin rudder would never stop the flat spin.  Holding full down elevator at the same time I applied full power would tend to cause the flight path to pitch down toward vertical or beyond during the recovery, so I soon decided that wasn't a good idea at low altitude.
At least one crash was caused by climbing so high that the battery was essentially drained and then kicking the model into a flat spin.  When the ground started approaching, I advanced the throttle to recover, but the battery didn't have enough power left to run the motor at all, so the flat spin continued to the ground.
The model happened to be a loose semi-scale model of a Piper Cub.  To be specific, it was the "Hobby Zone Super Cub S" or "LP" (essentially same the same aircraft).  No suggestion is intended here that a full-scale Super Cub or Piper Cub would behave the same way.
The model was set up with fairly modest control throws, and the story might have been different had they been larger, but at any rate they were large enough to enter a flat spin that could not be recovered from without adding power. I usually used some power for the spin entry, but it was possible to enter without power as well, though not completely consistently.
Changing the wing from the stock wing with dihedral and no ailerons to a modified wing with no dihedral and with ailerons didn't fundamentally change the spin recovery characteristics, at least if I left the ailerons centered.  (Notes on how the ailerons could be used to effect recovery from a flat spin without adding power are given here at this related ASE answer.)
In reference to a comment-- at the CG used to demonstrate intentional flat spins, the plane was definitely statically stable in pitch when trimmed for a wings-level glide near the minimum sink rate speed, though perhaps not by a large margin.
The take home lesson is -- when it comes to spins, your mileage may vary.  Never assume that spin characteristics will be similar from one airplane type to the next, or even from one example of a particular aircraft to the next.

Most of this entry is not exactly an answer, but we're really not supposed to use comments to provide information on this website, so I'll post it anyway.

Data presented here indicates the a staticly unstable model, as an unpowered Piper Cub should be a fairly docile glider, but matches an account of 2 characters who managed to flat spin a Cessna 152, and lived to tell the tale by applying full throttle when all else failed.

There can be extreme propeller effects at low speed and high power, type dependent of course.
For example, the very flat spins that you can see aerobatic aircraft do need engine power. This is a gyroscopic effect.
There are also torque, spiral slipstream and asymmetric propeller blade loading (P factor) effects all obviously greater with power on.
All conventional wisdom and all the aerobatic textbooks that I have read say the emergency recovery from an inadvertent spins starts with Power Off.
However my most recent (and comprehensive) aerobatic textbook advises that in the recovery from a deliberate flat spin that leaving the power on will make the recovery quicker. The reason given is that the extra airflow over the tail overcomes the nose-up gyroscopic effect.
I use the power on method from that book in my Pitts S1. It has worked quickly about 100 times so far.
However if I found myself is a spin that I had not deliberately started I would follow the Beggs-Muller Emergency Spin Recovery. Power to Idle, Let go of the stick and apply Full Rudder Opposite to the Yaw direction as determined by looking down the top of the engine cowling at the ground.
I know that any spin in the Pitts will stop by this method.

All aircraft respond differently in stopping a spin. The power off allows the nose to drop, upright or inverted, and also stops or minimizes gyroscopic forces. In entering a spin on purpose in an Extra, power can be kept on full, in-spin ailerons deflected, full opposite rudder, slightly less aft stick in an upright spin and the plane will recover very quickly. Inadvertent spin recovery can also be, power off, let go of stick, sight down nose directly over the nose, determine rotation and full opposite rudder and wait, depending on aircraft it could take a rotation or 2. That’s where pilots without training get in trouble. Also the opposite rudder is usually harder to push.


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Why does the Convair 990 produce this howling sound during landing?
Watching this video of a landing Convair 990, one can hear a whooshing howl at about 0:11-0:12, as it flares just prior to touchdown (not to be confused with the run-of-the-mill howling that you can hear from 0:13 on as the engines spool down after touchdown); what makes this sound?  Does the CJ805-23 engine have a different sound profile than other engines?

What you hear at 0:11-0:12 is just the sound of the engines being reduced to idle thrust, and the doppler effect as the aircraft passes your position.
I have heard that sound hundreds(maybe thousands) of times. It is very normal, and sounds just like all jets of that generation.
Here are more examples:
Skymaster DC-8-63F Landing
707 ! Touch & Go, Depature, Landing.
Boeing 707 Landing - Smokey!


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Why is the A330/A340's angle-of-attack protection disabled in alternate law, even if the AoA vanes are operating normally?
Reading about Air France Flight 447, to quote Wikipedia (emphasis added):

... A second consequence of the reconfiguration into alternate law was that stall protection no longer operated. Whereas in normal law, the aircraft's flight management computers would have acted to prevent such a high angle of attack, in alternate law this did not happen. (Indeed, the switch into alternate law occurred precisely because the computers, denied reliable speed data, were no longer able to provide such protection – nor many of the other functions expected of normal law).[55] The wings lost lift and the aircraft stalled.

But whether an aircraft stalls or not has nothing to do with its airspeed - the only things that matter are the wing's angle of attack and configuration (e.g., are the slats extended? is the leading edge damaged? have we got ice on the wings?).  The aircraft's configuration was completely normal, and the AoA vanes were unaffected by the blocked pitot tubes (as evidenced by the fact that the aircraft's stall warning correctly sounded due to its excessive AoA during the period of time that the pitot tubes were blocked and valid airspeed data was unavailable).  Why does the A330/A340 disable high-AoA protection in alternate law if airspeed data is lost - even if AoA data remains perfectly valid?

I've read a lot about the airbus stall protection and I am still not sure if it really controls angle of attack. I think it is more of a attitude and speed stabilization, which would be lost when pitot tubes fail.
See this video: https://www.youtube.com/watch?v=9fqy8uPzW90 at 10:20 he says: aoa may vary even with full aft stick but its the pitch and speed that they want to be stable


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Why was the Electra uniquely vulnerable to whirl-mode flutter?
The Lockheed L-188 Electra, notoriously, suffered from early problems with whirl-mode flutter, which caused two Electras to break apart in flight in 1959 and 1960, forcing an expensive redesign of the Electra's engine mounts and killing off Electra sales.
In contrast, the other similar quadturbopropliners of the era (Viscount, Britannia, Il-18, An-10, CL-44, Vanguard) - even those which entered service before the Electra ever flew - had no such problems.
Why?

The engineers did all the vibration analysis in lower precision arithmetic (double instead of quad, single instead of double), such that significant digits fell off the end of summands when the vibration matrices were processed. We covered this case in a numerical analysis class on matrix algebra.

Flutter is a natural frequency resonance phenomenon.  Something is oscillating, and its oscillation, at some point, starts to match the natural frequency of the structure it's attached to, and a mutual input/feedback cycle starts that stores and returns the energy in such a way that it magnifies the initial input and away you go.
The outer wing was the saxophone... the engine nacelle was the reed.
The other airplanes?  Well, when you get down to it, fortunately they were just out of tune you might say, so they weren't affected.

the forward structural section of the engine nacelle which supported the reduction gearbox for the propeller drive and connected the gearbox mounts to the rest of the engine supports were designed in such a way that if the plane made a hard landing, those structures would be weakened enough to allow the establishment of undamped whirl-mode flutter/resonance.
The dynamics were beyond the capabilities of the computer modeling tools available at the time, so the root-cause investigation of the crashes was based instead on the construction of precision scale models of the entire airplane which were then "flown" in a wind tunnel, with the tests captured on film with movie cameras.
In this way, the structural deficiency of the gearbox-and-engine mounts was uncovered.


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What are these engine gauges in the Comet 4 for?
What are these gauges on the Comet 4's engine-gauge panel (between the captain's and first officer's instruments, above the throttle levers), marked "POWER LOSS INDICATOR", for?  (Sorry for the blurry image.)

(Image cropped and annotated by me; original by Geni at Wikimedia Commons)
I'm assuming they're engine gauges of some sort, since there're four of them and they're located immediately below the engine RPM and EGT gauges (and above the throttle levers); could they be for monitoring engine performance during hot-and-high takeoffs?
They are apparently not present in the Comet 1, which instead has engine oil temperature/pressure gauges in this area (see pages 59-60 of this PDF, marked as pages 58-59).

They were used on takeoff to monitor engine performance. Takeoff power should result in the needles moving to the vertical marker and all engines should be registering the same reading.
The indicators monitor the pressure in the exhaust cone of each engine and will give a warning of failure which might in certain cases only become apparent by watching a combination of other instruments.

OK, but what do they actual monitor?

@MikeBrockington I have edited the answer to address your question.


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Why not use the yoke to control yaw, as well as pitch and roll?
(Inspired by this question about rudder hand control on joystick-equipped aircraft.)
Most civilian fixed-wing aircraft (post-1987 Airbus airliners being the primary exceptions) use a yoke (essentially a steering wheel mounted on a vertical column that can swing back and forward) to control pitch (pushing the yoke forward pitches the nose down; pulling the yoke back pitches the nose up) and roll (rotating the yoke clockwise rolls the aircraft to the right; rotating the yoke counterclockwise rolls the aircraft to the left), but control yaw via a separate set of rudder pedals (pushing on the left-foot pedal yaws the nose to the left; pushing on the right-foot pedal yaws the nose to the right).
If the yoke were used to control yaw as well as pitch and roll, this would allow the pilot to make coordinated turns using just their hands, rather than having to remember to push with one of their feet at the same time, and would eliminate the risk of accidentally applying the brakes when steering on the ground.
A couple of possible ways for yoke-based rudder control suggest themselves; one would be to tilt the column from side to side (tilting the column left would yaw the nose to the left; tilting the column right would yaw the nose to the right), while another would be to push one of the yoke's horns forward while pulling the other back, rotating the yoke about its vertical axis (pushing the left horn forward and pulling the right horn back would yaw the nose to the right; pulling the left horn back and pushing the right horn forward would yaw the nose to the left).
Here's an illustration of what I've in mind:

Why don't any aircraft use the yoke to control all three axes, rather than just pitch and roll?

User interface is the last thing you want to change on any product. It's like why are we still using the QWERT keyboard and why we cars still use steering wheels.

@Undo South Park discovered such a solution in season 5

@Undo, a handlebar. Particularly one in which the steering effect is controlled or moderated by force (but this applies to wheels as well). Which is to say it would be a hand-driven rudder, except that it works in the opposide sense. Arguably, the Formula 1 'steering wheel' is effectively a handlebar, never requiring a change of grip and rarely exceeding a ±90° turn.

The modern control yoke is directly derived from the "joystick" control that became standard on aircraft in the days when Glenn Curtiss personally ran the company that was the main competitor to the Wright brothers.
After inventing aileron control (the Wrights were still using wing warping at the time -- this was before 1910), Curtiss needed a way to control movement of the ailerons, and subsequently of the rudder.  The original 1903 Wright Flyer had the wing warp controlled by sliding the pilot's platform (a flat surface, on which the pilot lay prone) right and left, and coupled the rudder, so that roll and yaw were inseparable.  Curtiss decoupled them, and needed to add a third control -- and since he was also sitting upright, even in his first airplane, his feet were available.
Running the elevators and ailerons on the control stick was obvious, and it was equally simple to put one's feet on a bar that directly operated the rudder -- and this layout became the standard almost instantly.  Even the Wrights adopted it before they demonstrated their Flier to the Army.
Over time, there have been a few examples of variations.  Airplanes that brought back coupled rudder and aileron, like the Ercoupe, let the pilot fly with "feet flat on the floor" -- and it seems to me there was at least one design, from the biplane era, of a transport aircraft with rudder operated much the way you describe; a control wheel mounted on a joystick, with stick movement controlling roll, and wheel rotation controlling yaw.
The fact this has only appeared in a very small number of designs suggests that, as noted in a comment, it's a bad idea to change something that's been long standardized -- yet, we have a good number of aircraft, ranging from sailplane to jet fighter and large transport, that use "sidestick" -- in which, in the transport case, the pilot in command actually flies with his left hand, while the copilot flies with his right.  Joysticks continue in wide use as well, especially in smaller or higher performance aircraft, or those with ejection systems.
The other, and I believe the main reason we don't see control schemes like what you describe is that it becomes impossible to maintain precise, separate control of roll and yaw.  When the same pair of hands are doing both jobs, the brain will mix them together, or in trying not to, will reverse mix (leading to a forward slip or a skid, the latter widely considered very hazardous at low altitude and speed).  If you have an aircraft in which it's difficult to avoid mixing either adverse or proverse rudder while applying aileron, it'll be difficult to land or take off in crosswinds, hard to maintain a precise final approach, and nearly impossible to fly high precision maneuvers (like air to air refueling or tight formations).

I have a joystick for PC that has a third axis. It's always disabled because it's physically all but "impossible" (+1) not to yaw while pitching.

@Mazura : Now add turbulence while trying to not do that!

@Mazura: interesting. The opposite happened to me: coming with significant real-life experience  (gliders) I expected that flying a PC simulator  without pedals and instead twisting the stick would be weird; but instead it felt natural almost instantly.

@MartinArgerami A lot of it comes down to where the stick is positioned and how it's set up with regard to null zones and such. It will be a lot harder to bank without accidentally yawing if the stick is directly in front of you than if it's over to the side where your arms naturally reside.

@Martin - my 3rd axis would have to turn much farther and have a huge dead zone, or better resistance to turning (both of which are insane to intentionally introduce into a control system). I had high hopes for it, and in a flight sim or a small plane it might be cool. But trying to put a reticule on target ("impossible to maintain precise ... control") or landing a real 747, idts...

@Vikki, and ZeissIkon -- Along the same lines -- some radio-control model airplane fliers use what is called "Mode 1", where the right-hand stick controls ailerons and throttle, and the left-hand stick controls rudder and elevator.  This is said to be more precise than putting both of the primary controls (aileron and elevator) on the right stick.  Perhaps it originated from rudimentary systems where a knob or lever only controlled one function, so having two moving control surfaces automatically meant having two different controls.

It's just a bad idea Sean.  Believe me if you've done any flying you would NOT like a control column that you have to shove sideways, or a twisty yoke, for rudder as well as roll and pitch. Your feet are sitting there doing nothing anyway.  And you need to be able to control it one handed so you can work the thrust levers or power levers or throttles with the other.  How would you work such a column with one hand?
Plus, in any transport airplane with a yaw damper system you never touch the rudder pedals once airborne unless an engine quits.  And if that happens you'll be glad you have your upper thigh muscles to the do the work of holding in rudder input for an extended period, and not your forearms already busy with 2 other jobs.
I'm imagining trying to hold a yoke pushed to the side following an engine failure on rotation, while also controlling pitch and roll with it, while my feet sit on the floor being useless... very unpleasant.
Where it might be viable is with a side stick FBW controller where the stick rotates for yaw, like a computer joystick. But even there, I'd rather have my feet do it.

It can be done with one hand. Lots of PC joysticks do it. That said, I prefer the pedals.

Such designs do not work well when the rudder is required other than during turns.
A typical situation would be the use of rudder to counter the p-factor (asymmetric turning tendency) on propeller aircraft.  After take-off, one might need to apply a significant amount of rudder during climb at high-power and high-AOA.
It would be very inconvenient to have the yoke "tilted" or "twisted" during the climb, even when the aircraft is not turning at all.

Both of your designs would be impossible to use with one hand, which would make them impractical to use, since you need a free hand with which to manipulate other cockpit controls.
The first design (move the entire yoke left and right in order to yaw) is less bad, in that it's still possible to use one-handed as long as the yoke is nearly horizontal (ailerons neutral). But if you have the yoke turned 90 degrees, now it's nearly impossible to control both the ailerons and the rudder, because both of those controls use the same hand motion (namely, moving your hand left and right). This is less important in the air, where large aileron inputs are relatively uncommon, but when taxiing with a crosswind, you do often want to give a large aileron input and a rudder input at the same time, and often in opposite directions.
The second design (yaw the yoke in order to yaw) would make the yoke nearly impossible to use one-handed under any circumstances. It would be very difficult to give elevator input without rudder input, or rudder input without elevator input.
Besides, what else am I going to do with my feet? :)

"But if you have the yoke turned 90 degrees, now it's nearly impossible to control both the ailerons and the rudder, because both of those controls use the same hand motion (namely, moving your hand left and right)."  No, they don't; the ailerons involve rotating the hand and lower arm, while the rudder involves moving the hand and lower arm without rotating them.

@Sean But depending on the forces and lever arms involved, that would require you to exert a huge amount of torque on the yoke using your hand.

There are a bunch of setups for disabled pilots where everything is on the yoke, including pitch, roll, yaw, and throttle. The Sky Arrow LSA has a hands only configuration as a purchase option (functions split between hands).

The main thing for a non-disabled pilot is it seems a shame to waste the feet by not having them controlling something.

I believe that combining the controls all into the yoke could lead to more problems than pilot adjustment, particularly outside of fly-by-wire systems. The yoke basically becomes a full single-point-of-failure for all of your controls in the case of some catastrophic yoke-snapping incident. I don't expect anybody to approve a reduction in redundancy, particularly in flight-critical components.


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Are there any aircraft where minimum-V1 is limited by Vmcg?
V1, unlike all the other Vspeeds, is not rigidly determined by the laws of physics, the aircraft’s specific abilities, and the conditions of the particular takeoff being attempted,1 but is, rather, chosen by the pilots from a range of possible V1s.

The lower limit of this range is generally set by the speed past which the takeoff can safely be continued while maintaining adequate obstacle clearance, even in the event of an engine failure (henceforth known as the first-safe-go speed).
The upper limit of this range is set by the speed past which the aircraft can no longer be guaranteed to stop on the runway in the event of a maximum-effort no-reverse-thrust rejected takeoff (henceforth known as the last-safe-RTO speed).

However, if an aircraft is sufficiently light and has sufficiently-powerful engines (especially if said engines are mounted far from the aircraft’s centerline), one could potentially conceive of a situation where the lower limit of the V1 envelope is not, in fact, determined by the first-safe-go speed, but, rather, by...

...the speed below which the aircraft has insufficient rudder authority to maintain directional control at takeoff thrust in the event of an asymmetric engine failure (known as the minimum controllable speed - ground, or Vmcg).

Such a light, sporty aircraft could easily have a theoretical first-safe-go speed that is lower than Vmcg, as low total weight and high thrust-per-engine both decrease the first-safe-go speed,2 and, simultaneously, increase Vmcg.3  This would force the lower limit of the possible-V1s range to be set, not at the theoretical first-safe-go speed, but, rather, some distance above that, at Vmcg (as an asymmetric engine failure at or above the theoretical first-safe-go speed, but below Vmcg, would result in an immediate loss of directional control, necessitating a rejected takeoff).  For added complexity, some aircraft have engines at varying distances from the aircraft’s centerline (for instance, a trijet with one engine slung under each wing and one mounted in the tailcone, or a quadjet with one outboard and one inboard engine slung under each wing), resulting in different Vmcgs for different engine-out scenarios, such that, at a given speed, an aircraft might be able to safely continue a takeoff if a centerline or close-to-centerline engine fails, but would suffer a loss of directional control, and have to reject, should a far-from-centerline engine fail.
Are there actually any aircraft for which the minimum-allowable-V1 is limited by Vmcg, rather than the first-safe-go speed?

1: ...except in the special case of the aircraft being at exactly its maximum allowable weight for the takeoff being attempted, in which case there is only one possible value of V1.
2: ...as a lighter aircraft needs less speed (and, thus, less thrust) to become airborne, and an aircraft with powerful engines has more thrust to work with in the event of an engine failure.
3: ...as an aircraft with powerful engines needs more rudder authority (and, thus, more speed) to maintain directional control with an asymmetric engine failed and the other(s) at takeoff thrust (a problem which grows steadily worse the further the asymmetric engine(s) get from the aircraft’s centerline, due to the larger and larger yawing moment arm generated as they move away from the centerline), and a lighter aircraft has less weight on its landing gear (and, thus, less traction force acting to resist the yawing moment from an asymmetric engine failure).

Yes
Almost any transport category jet will reach its Vmcg V1 limit in favorable conditions.
The rationale is quite easy: When fully loaded with heavy fuel load (ie. at maximum takeoff weight) some 20% of weight is payload and about 20% is fuel. When the same jet is taking off with light passenger load for a short hop with low fuel load, there is massive surplus of thrust available so there is some acceleration available in case of engine failure on ground. This is especially true for twins.

A commonplace situation for Vmc to be limiting is when V speed reductions are used for wet or contaminated runway situations.

Astoundingly, the published short field takeoff procedure for the PA-34 Seneca calls for taking off below Vmc. See this excerpt from page 6-7 of the operating handbook:

When the shortest possible ground roll and the greatest clearance distance over a 50-foot obstacle is desired...[snip]...accelerate to 70 MPH and rotate firmly so that when when passing through the 50-foot height the airspeed is approximately 80 MPH. Retract the gear when a gear down landing is no longer possible on the runway.
It should be noted that the airplane is momentarily below Vmc when using the above procedure. IN THE EVENT THAT AN ENGINE FAILURE SHOULD OCCUR WHILE THE AIRPLANE IS BELOW Vmc IT IS MANDATORY THAT THE THROTTLE ON THE OPERATING ENGINE BE RETARDED AND THE NOSE LOWERED IMMEDIATELY TO MAINTAIN CONTROL OF THE AIRPLANE.

It is not astonishing as you might first think. Class B light twins are not required to demonstrate any single engine performance below 50ft and before landing gear has been retracted. You may find some performance graphs from AFM relates to accelerate-stop-distance etc. but they are not comparable to transport category aircrafts’ requirements and may include shady procedures and speeds as you described.